Method and apparatus for delivering chemicals to a well head

ABSTRACT

A pump controller for electrical connection between a source of chemical supply and a DC powered chemical injection pump of the type having a reciprocating piston or diaphragm for delivering a quantity of chemical to a well head after each compression stroke of the pump, the controller including: 
     a switch operable to sequentially deliver activation current to the pump; 
     a voltage sensor between the pump and the switch to extract DC voltage signals indicative of activation of the pump, 
     an analogue-to-digital convertor for converting the sensed DC voltage signals into digital format; 
     a digital signal processor operative to differentiate DC stroke voltage signals from the sensed voltage signals, thereby to indicate the occurrence of each stroke; and 
     a switch controller programmed with pump parameters and target chemical delivery dosages to sequentially deliver activation current to the pump, measured or calculated from the digital DC stroke voltage signals, and hence chemical delivery to the well via the injection pump at required intervals.

BACKGROUND OF THE INVENTION

This invention relates to well heads such as those used to extract oil from the ground and to inject into the well head a required amount of chemicals at regular intervals by means of a displacement pump in order to improve the efficiency of the extraction process.

The injection of chemicals into a well head is conventionally undertaken by high pressure reciprocating pumps which draw small, discrete, amounts of liquid chemicals from a storage tank at timed intervals, such as one to ten cycles per minute, each cycle typically lasting one to six seconds, for delivery to the well head at a pressure of up to 6000 p.s.i., the operation being controlled by a pump controller sending activation current to the pump motor, being a DC commutator motor where the current is supplied by a rechargeable battery, which may typically be re-charged by means of a solar panel. Whilst such an arrangement is generally cost effective in areas where mains electricity is unavailable it will be apparent that the DC battery voltage can vary significantly during each 24 hour period. Where there is insufficient voltage available to the pump, such as at night, it can lead to the target dosages of chemicals to the well head being missed, which, in turn, leads to under-dosing and hence inefficient use of the chemicals and inefficient oil extraction from the well head itself. In contrast, where the battery is fully charged such as during the middle of a sun-lit day, this can lead to an over-dosing of expensive chemicals to the well head. Each such occurrence represents an unwanted financial loss to the oil extraction process. The foregoing disadvantages can be overcome by the use of a flow meter downstream of the pump by which an actual volume of liquid chemical delivered to the well head can be measured. However, this adds to the cost of the installation and represents, along with its attendant circuitry, an additional drain on the battery. Another disadvantage is that the flow meter can also become clogged and malfunction.

The present invention is derived from the realisation that the voltage variations inherent in battery-powered DC pump delivery systems which are time-based are not conducive to accurate delivery of the chemicals and there is a need for an alternative approach which is volume-dependent as opposed to time-dependent.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a pump controller for electrical connection between a source of chemical supply and a DC powered chemical injection pump of the type having a reciprocating piston or diaphragm for delivering a quantity of chemical to a well head after each compression stroke of the pump, the controller including:

a switch operable to sequentially deliver activation current to the pump;

a voltage sensor between the pump and the switch to extract DC voltage signals indicative of activation of the pump,

an analogue-to-digital convertor for converting the sensed DC voltage signals into digital format;

a digital signal processor operative to differentiate DC stroke voltage signals from the sensed voltage signals, thereby to indicate the occurrence of each stroke; and

a switch controller programmed with pump parameters and target chemical delivery dosages to sequentially deliver activation current to the pump, measured or calculated from the digital DC stroke voltage signals, and hence chemical delivery to the well via the injection pump at required intervals.

With this arrangement even though there is little or theoretically no return electrical signal from the DC motor driving the pump, other than continuous background voltage noise from the commutator brushes of the DC motor, by extracting what other signals are present apart from the commutator noise and correlating them to the rotational speed of the pump, highly accurate delivery of chemical dosage can be achieved based upon the number of strokes of the pump that are counted during each delivery sequence, the total dosage delivered in each sequence being the sum of the volume of chemical injected at each stroke and the number of strokes, irrespective of the voltage available from the battery.

Conveniently, the means to generate pump stroke voltage signals indicative of strokes of the pump is shunt resistor.

Conveniently, the means to generate pump stroke voltage signals indicative of strokes of the pump is a Hall-effect device.

Conveniently, the pump controller is battery operated, such as by being connected directly or indirectly to a battery supplying activation current to the pump motor.

Preferably, the digital signal processor means includes one or more band-pass filters whereby to differentiate stroke voltage signals from background voltage signals from e.g. the commutator of the pump motor. Such signal differentiation can be further enhanced by mathematical modelling using known tools such as Fast Fourier analysis, digital band pass filtering and other numerical transformation methods.

According to a second aspect of the invention there is provided a method of controlling delivery of chemicals from a DC powered reciprocating chemical injection pump to a well head, the method including the steps, in any convenient order, of collecting voltage analogue signals indicative of activation of the pump from the DC motor of the chemical injection pump, thereafter converting the voltage signals to digital signals and analysing the digital signals to identify successive strokes of the pump, using the counted strokes to indicate when a required amount of chemical has been delivered to the well head, and thereafter deactivating the current to the pump for a selected time period, the sequence continuing whereby to regularly provide measured or calculated volumes of chemical to the well head via the injection pump

According to a third aspect of the invention there is provided A method of delivering a required amount of chemical to a well head from a chemical storage tank having an associated chemical volume gauge graduated to provide an indication of volume of chemical deliverable to the well head via an associated displacement pump, the method including the steps of disconnecting the chemical storage tank from the gauge, taking a reading of the gauge as to quantity of chemical in the gauge and thereafter activating the pump for a given number of pump strokes measured or calculated in accordance with the second aspect of the invention, thereafter taking another reading of the gauge to determine the volume of chemical remaining in the gauge and hence quantity of chemical delivered to the well head per stroke from the gauge, thereafter reconnecting the chemical storage tank to the pump and sequentially delivering the required volume of chemical to the well head at predetermined intervals by reference to pump strokes over time.

Conveniently, the chemical volume gauge is a graduated sight glass.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic view of a conventional prior art chemical delivery system to a well head, and

FIG. 2 is a schematic view of a chemical delivery system to a well head in accordance with the invention, and

FIG. 3 is a graph showing DC current variation during each stroke of a chemical delivery pump.

DETAILED DESCRIPTION OF THE DRAWINGS

Turning firstly to FIG. 1, a well head assembly shown generally at 1 is shown hydraulically connected to a chemical storage tank 2 which provides regular doses of chemicals to the well head 1 via a 12 volt DC driven reciprocating pump 3 having a DC commutator-type motor.

The pump 3 is powered by a 12 volt rechargeable battery 4 connected to a solar panel 5 by which it can be recharged during daylight hours. Between the pump 3 and battery 4 is a pump controller 6 which includes a timer 7 for regulating when the pump 3 is switched on or off via a switch 8.

In operation of this prior art system the voltage available from the battery 4 typically ranges from between about 11.5 volts to 14 volts but may be considerably lower depending on the charge level of the battery 4. This, in turn, affects the power available to the pump 3 and hence the amount of chemical it is able to deliver within each specified time period. As a consequence chemical delivery to the well head 1 can be highly variable, leading to inefficiencies in the case of under-dosing of chemicals due to low battery voltage or over supply of chemicals where the battery voltage is at its highest, thereby wasting commercially valuable chemicals in the process.

In contrast to the foregoing prior art system the present invention as illustrated in FIG. 2 does not depend upon time-based delivery of chemicals to the well head 1 but instead depends upon the amount of pump strokes detected during each delivery sequence. This is achieved by a pump controller circuit shown generally at 9 which includes a solid state switch 10, such as a MOSFET switch, interposed between the battery 4 and the pump 3. Between the MOSFET switch 10 and the pump 3 is a current sensor in the form of a resistor and, in particular, a shunt resistor 11 which is therefore able to feed DC noise signals from the commutator of the pump motor as well as low-voltage (millivolts) signals generated by the pump 3 during each compression stroke to a signal amplifier 12 and then to an analogue-to-digital converter 13 permitting the digitised signals to be analysed by a digital signal processor 14 which is able to differentiate between relatively high voltage background signals resulting from e.g. the commutator of the pump motor 3, and the lower voltage signals indicative of each compression stroke. This signal differentiation is possible because the motor 3 consumes more power when the pump is in compression mode than when the pump stroke is in induction stroke mode, i.e. when it is sucking in chemical from the tank 2 prior to injecting it under pressure to the well head 1. This is illustrated in FIG. 3, which shows motor current variation between each stroke of pump 3. Such signal processing may use any suitable band-pass filtering and noise suppression techniques including Fast Fourier analysis and other numerical transformation methods. Similarly, although a resistor, such as shunt resistor is used as a current sensor in order to extract the voltage signals from the motor, other suitable means may be used, such as for instance a Hall effect sensor. Thus, by the signal processor 14 differentiating between background voltage and successive compression strokes of the pump 3, these strokes can then be counted to establish the exact number of strokes during each chemical injection cycle and hence an exact amount of chemical injected into the well head 1 during each such cycle.

These digitised compression stroke signals are relayed to a pump switch controller 15 which receives or into which is programmed pump parameters 16 giving, for example, the volume of chemical dispensed after each compression stroke of the pump 3 and target chemical delivery information 17 by which the dosage of chemicals being delivered to the well head can be both monitored and adjusted, either on site or remotely via a cellular of satellite gateway. In this way the pump switch controller 15 is therefore able to provide switching instructions to the solid-state switch 10 for turning the pump 3 on as required during each cycle which may, accordingly, be of varying duration depending upon the charge state of the battery 4. Thus, each chemical dosage delivery cycle is independent of the time taken so that on the completion of a required number of compression strokes from the pump 3 each injection cycle ends with a known quantity of chemical having been delivered to the well head 1. This has considerable advantages over the prior art time-based delivery system discussed with reference to FIG. 1 and has the further advantage in that the pump control circuitry 9 can be located away from the classified hazardous area around the well head 1. The system is therefore ideally suited for retro-fitting to existing well head installations which currently rely upon time-based delivery of chemicals to the well head 3.

The chemical itself is delivered by means of a reciprocating displacement pump, usually an electrically powered piston and cylinder-type pump which delivers a set volume of chemical corresponding to the largest volumetric size of the cylinder when the piston is at its down-stroke, before the piston then pumps the chemical into the well head during or at the top of its up-stroke. Whilst this chemical delivery arrangement is mechanically relatively simple and reliable it suffers from a problem in that it generally does not take into account variables such as the type and size of the pump, the working pressure at the well head and any other variables making the delivery of chemicals to the well head difficult to measure and administer accurately. For example, conventional technology uses a flow meter pulse count to detect and estimate the amount of chemicals being delivered to a well head, but at low flow rates there are large inaccuracies and, in addition, the flow meter itself can clog up, leading to the adoption of an alternative strategy, that of using timers to meter out estimated quantities of chemicals to the well head. However, all well heads are different, operating at different pressures, using different pumps for injecting chemicals into the well head and having other variables which make it difficult to administer an accurate amount of such chemicals to the well head at pre-selected intervals. Hence, the delivery of chemicals to well heads in a controlled and accurate manner can be considerably improved by calibrating the discharge from a chemical volume gauge graduated to provide, typically, a visual indication of volume of chemical being delivered to the well head irrespective of the accuracy of the gauge or other variable parameters such as the efficiency of the pump and the pressure at the well head.

Accordingly, with the ability to detect pump strokes for delivering set quantities of chemical at each stroke the invention also extends in a third aspect to a method of delivering a required amount of chemical to a well head from a chemical storage tank having an associated chemical volume gauge, such as a sight gauge, graduated to provide an indication of volume of chemical deliverable to the well head via an associated displacement pump, the method including the steps of disconnecting the chemical storage tank from the gauge, taking a reading of the gauge as to quantity of chemical in the gauge and thereafter activating the pump for a given number of pump strokes, thereafter taking another reading of the gauge to determine the volume of chemical delivered to the well head per stroke from the gauge, thereafter reconnecting the chemical storage tank to the pump and sequentially delivering the required volume of chemical to the well head at predetermined intervals by reference to pump strokes.

With this arrangement a very accurate measurement of chemical delivered to the well head per stroke of the pump can be obtained by e.g. visually inspecting the sight gauge while the chemical tank is disconnected from the gauge in order to calibrate delivery per stroke. When the pump is then reactivated and the pump strokes counted as the gauge loses chemical to the well head the pump can then be deactivated before the gauge is empty, thereby allowing the volume of chemical dispensed to the well per stroke to be easily and accurately determined and the tank can then be reconnected. 

1. A pump controller for electrical connection between a source of chemical supply and a DC powered chemical injection pump of the type having a reciprocating piston or diaphragm for delivering a quantity of chemical to a well head after each compression stroke of the pump, the controller including: a switch operable to sequentially deliver activation current to the pump; a voltage sensor between the pump and the switch to extract DC voltage signals indicative of activation of the pump, an analogue-to-digital convertor for converting the sensed DC voltage signals into digital format; a digital signal processor operative to differentiate DC stroke voltage signals from the sensed voltage signals, thereby to indicate the occurrence of each stroke; and a switch controller programmed with pump parameters and target chemical delivery dosages to sequentially deliver activation current to the pump, measured or calculated from the digital DC stroke voltage signals, and hence chemical delivery to the well via the injection pump at required intervals.
 2. The pump controller of claim 1, wherein said voltage sensor is a shunt resistor.
 3. The pump controller of claim 1 wherein said voltage sensor is a Hall-effect device.
 4. A pump controller according to claim 1 wherein the pump controller is battery operated, such as by being connected directly or indirectly to a battery supplying activation current to the pump motor.
 5. A pump controller according to claim 1 wherein the digital signal processor includes one or more band-pass filters whereby to differentiate stroke voltage signals from background voltage signals from the pump motor.
 6. A method of controlling delivery of chemicals from a DC powered reciprocating chemical injection pump to a well head, the method including the steps, in any convenient order, of collecting voltage analogue signals indicative of activation of the pump from the DC motor of the chemical injection pump, thereafter converting the voltage signals to digital signals and analysing the digital signals to identify successive strokes of the pump, using the counted strokes to indicate when a required amount of chemical has been delivered to the well head, and thereafter deactivating the current to the pump for a selected time period, the sequence continuing whereby to regularly provide measured or calculated volumes of chemical to the well head via the injection pump.
 7. A method of delivering a required amount of chemical to a well head from a chemical storage tank having an associated chemical volume gauge graduated to provide an indication of volume of chemical deliverable to the well head via an associated displacement pump, the method including the steps of disconnecting the chemical storage tank from the gauge, taking a reading of the gauge as to quantity of chemical in the gauge and thereafter activating the pump for a given number of pump strokes measured or calculated in accordance with the second aspect of the invention, thereafter taking another reading of the gauge to determine the volume of chemical remaining in the gauge and hence quantity of chemical delivered to the well head per stroke from the gauge, thereafter reconnecting the chemical storage tank to the pump and sequentially delivering the required volume of chemical to the well head at predetermined intervals by reference to pump strokes over time.
 8. A method according to claim 7 wherein the chemical volume gauge is a graduated sight glass. 